The Home Repair forum is pretty active. If no responses here, you might try there.

Probably need more info. I just redid my sidings and on my back screened in porch, we used a vinyl beadboard that they use for mobile home skirting. it goes vertical as opposed to the horizontal siding next to it. I would say go to a lowes, menards or Home Depot and just look around the siding area, there are lots of ideas.

I can't speak from personal experience, but I did some research on porch enclosures for a house we're looking to build next year that you might find helpful. We're currently looking at a system made by Harvey Industries http://www.harveybp.com/product.aspx?pid=8&shape=14 which is extruded aluminum. These are purpose built, pricing starts around $60/foot of enclosure. Others: 1: Frame porch to allow wood screen door panels to be inserted, see http://www.thisoldhouse.com/toh/article/0,,1541906,00.html for a description. Lots of door choices ranging from wood to vinyl. There are purpose built mounting kits http://www.screentight.com/prod-screen-doors-vinyl-doorpanelenclosure.shtml and acrylic panel kits http://www.screentight.com/prod-screen-doors-vinyl-windbreaker.shtml available for certain doors. 2: Removable Aluminum/Fiberglass Porch Panels - see http://www.qualitywindowscreen.com/store/patio-porch-screen-systems-patio-porch-screen-panels-c-101_176.html for an example. Not sure about glass on these. 3: Screentite and similar. See http://www.screentight.com/prod-screen-tight.shtml or this one which allows windows: http://www.kaufmannwindow.com/porch.html. 4: Inexpensive vinyl sliding glass doors. See http://www.thehouseofwindows.com/Sliding_Glass_Patio_Doors_p/snc5068.htm for what would likely be a true 3-4 season porch but expensive.

I looked at all the vinyl window options and came across energy wise manufacturing out of Schullber, WI. I could not be happier w this product! I have been wanting a screened in porch for many years, but could not justify the cost if it was not used "most" of the year. I live in Richmond, VA where we have mild winters and it is not uncommon to have sunny 60 degree days in Dec/Jan/Feb. These windows create a "greenhouse effect" and allows me to enjoy my screened in porch most of the year. Alot of people thought this idea was crazy - but I am glad I stuck with it and found a company that makes them and was willing to ship them to me. Besides for retaining heat in the winter, I really enjoy the fact that the room stays clean from dust and pollen most of the time. Some people balked at the idea of taking them in and out, and also storing them. But for me it’s worth the trade off. The shipping cost is high ($300.00) especially in my case bc my window openings were SO LARGE (60 X 66). An added bonus is that the shipping container acts as a heavy duty storage container for the windows when not in use. I store the container under my deck. Eugene is a great guy and extremely responsive to his customers! This a unique product and for people who don’t mind the effort, it is the perfect solution to get more use out of a screened in porch. I would HIGHLY RECOMMEND!