I would think the weight of a single clematis would not be so great as to require this. I have a 6'X6' trellis where I first planted an Asao clematis, then a Lady Banks rose. We did sink our supports with concrete so that I could have the versality of planting what I wanted on it. It will soon be home to 2 different clematis as well (Palette and Duchess of Albany). The weight bearing capability of the trellis makes this kinds of arrangement possible. I also have another trellis (8'x4') where I did the same thing--built the trellis using concrete, then planted according to the weight bearing capabilities of the trellis--it now houses a cl. hydrangea, precisely because it can handle that kind of weight. I have also added a Lemon Zest honeysuckle and a see a clematis in its future. :) I like to have versatility-but it's a personal decision whether to concrete or not.

If you're using the TEC, there's no need for the denatured alcohol, OR the tape. These are the things needed if using the silicone. All you need, is a caulking gun, a piece of cardboard, a bucket of clean water, and a grout sponge. Lay in your bead of caulk with the caulking gun. Then take your finger, and smooth it out, removing the excess, and wiping it off on the piece of cardboard. then take the sponge, and wring it out well, and then wipe the joint. You'll only be able to go a foot or two with each wipe, and you'll probably have to rewipe it once or twice to get a nice clean uniform joint. But do not wipe more than once with any part of the sponge, without rinsing it out well, first. You may even have to "massage" the sponge in the water to remove the caulking from the face of it, but it WILL come off so you can hit the joint with a clean sponge again.

The 100% silicone caulk (eg, GE brand) performs amazingly in wet areas for superior water resistance and adhesion. Paint will not stick to it. It does have a learning curve to apply it though - for any homeowners using it, watch some youtube videos for help. I personally like the 'windex trick' as well as using clorox wipes for cleanup instead of dry paper towels. The only problem I have found with silicone is it gets dusty and seems to stay a bit moist/tacky, so for ease of cleaning purposes, I wouldn't use it outside of the actual wet areas. For that yes you want paintable caulk, I usually get the longest life kitchen/bath caulk. After looking at your pics a bit more thoroughly, it looks like you should be alright with some quality paintable bath caulk, it will probably say 'siliconized' on the label, but you do want paintable. Even if you don't end up painting it, it won't retain that tackiness and be easier to clean.

@David Jensen - stained concrete is stunning! And it has a price tag. You do not just stain it and walk away. Concrete is porous (which is why it takes stains so nicely/easily...which is a draw back with red wine). It MUST receive some sort of finish. Please remember that commercial settings have NIGHT CLEANING STAFF that have RIDE-ON cleaning/polishing machines that get brought out several times per week. The concrete floors in Costco do NOT stay that "pretty" all by themselves. They take a crew of people riding along on those cleaning machines that clean at the front and leave polish behind out the back. Kinda like a tile/cement Zamboni. I see them in malls all over North America. Not many homeowners have that level of cleaning time/money/effort/machinery. It doesn't mean you CAN'T have stained conrete....it just means you will need to make some decisions. The FIRST decision is: How much MAINTENANCE are you willing to put up with? Can you handle a twice yearly polishing event (wax on, wax off grasshopper) that has to occur no matter how much you hate doing it? If you don't mind this idea, then you are one of the lucky one's. You get to have the "cheap and cheerful" stained concrete + urethane + wax finish. A single colour + urethane is in the $5-$7/sf range. If you do NOT want that type of hassle, then you have to step up your game and move into the epoxy finishes. A simple "clear/shiny" epoxy is $5-$7/sf. If you add the stain then you add another $2-$3/sf. That's where you get into the $10/sf range without much effort. If you want an exotic tri-colour stain then you get to $15/sf without blinking. If you want a picture of a beach at sunset then you will need to break out the big bucks = $25/sf! That brings us to your next decision: How much of a budget do you have? Again, the BASIC concrete floor (no stain) is $5/sf (that's some grinding, microtopping + polish + urethane finish). That one DEFINITELY will have serious amounts of maintenance. Lots of liquid polish+ lots of "stripping" old polish so that new stuff can be put down. Some of the most artistic floors are concrete. I think they are amazing. I also know the amount of artistry needed to get them into the "amazing" range is not cheap. I respect the process and - if I wanted a concrete floor - I would be more than willing to pay for that process. What often occurs is the homeowner thinks a finished concrete floor is a cheap way to get flooring. They think it will be bullet proof without ANY issues at all. How wrong they are. How very wrong and how bitterly disappointed they become when they realize an UNSEALED concrete floor (polished without finish) will stain and etch FASTER than marble. Again, Homeowner Know Thyself. Answer the questions: How much maintenance are you WILLING to do? How much budget do you have?