A vapour barrier under the subfloor or laminate will trap moisture. A vapour barrier under the floor will not stop condensation on the ceiling of the crawlspace and movement of the moisture into the floor above. Converting the crawlspace into a conditioned space will avoid moisture problems. Here is a link that might be useful: Conditioned Crawlspace Construction

You might look into double sided alum radiant barrier. Commercial extra tuff version will be about .006 and have cross linked poly stuff inbetween the alum. About 90# tear strength is what some I've bought says. Bugs arent going to like it and it hurts the little critters teeth to chew on it. Heat always goes to cold so it'll mirror the heat which fakes heat transfer and heat will mostly stay on the hot side.

You can try sealing seams in the plastic, and then sealing to tot eh foundation. Fastening to the foundation usually the harder part. I have used various 'plastic' boards (including ones designed for decks) fastened to the inside of the foundation with siliconized latex caulk behind the boards to seal there. The plastic is then sealed to the face of the board. If you use deck width boards you can usually rip them at least in half, and sometimes narrower if you then treat them gently.

Here's how I would approach your situation: a. Read the great article on conditioning crawl spaces as with removal of the exterior vents, you inadvertently started down this process, which imho, is a good process. Here is the great article: Martin Holiday: http://www.greenbuildingadvisor.com/blogs/dept/musings/building-unvented-crawl-space b. Lay down the minimum 6 mm water vapor over the crawl floor. I did this myself and it wasn't very hard: Lowes and HD sell it. Just overlap the edges and use the water proof tape, ideally bringing it up the concrete walls 10 inches or so and securing it. If you can't do the later, just lay it all the way to floor-wall junction with no exposed dirt, until you can do it as it (water membrane over all exposed dirt) is like the main pivotal step in controlling humidity of the crawl space. It's all reviewed in above article. c. Get your HVAC guy back to cut a small 3" or so supply vent circular hole in your metal duct. This plus him connecting a return duct to a floor above the crawl should provide enough air exchange. The numbers of cfm are above. If he truly won't (and he should read Mr. Holloway's article and answer why not) then perhaps you need a new HVAC man as this is established crawl space conditioning components. Remember that "perfect is the enemy of good enough". It all sounds complicated, but you've already done the hard part: removing the vents, insulating the rims. Now just lay the waterproofing vinyl membrane and try to get some air active exchange through there and you will be way beyond what most crawl space owners have done to ameliorate crawl spaces. Then sit back and take pleasure in your Home Owner accomplishment! Regards, SW.