I am rebuilding my whole frame. I had to pull the plywood bottom off of the base also, as it was rotting. The base was raised a bit with 4, 4x4 footings. My question is, can I just lay another piece of plywood on the base of the tub and rest the whole weight of the tub on that plywood¿

You can pretty much do anything you want to do with it. A lot of this depends on how large and sturdy your existing shell is though. If your seats or other areas exhibit thin areas of fiberglass structurally, then you may need to add additional support there. But for the most part most - (note the word 'most', doesn't mean 'all'! ) shells made from fiberglass can just stand on their own, with no skirt, nothing, and all they need is something to sit on (the footwell), and some stubs to keep them from tipping over.

Adding GOOD plywood, as in exterior grade is a bit expensive, but it will help to maintain a clean environment underneath, and help to contain your heat. And that's the key - exterior grade.

Here's something I wrote a while back, it might give you some other ideas as well: http://spasupport.com/support/skirt.html

Thanx for your help.
I have read your article. Great work btw.

I've been meaning to post some pics on how my building of the base went. Thanx for the plans, they worked awesome.

#2

#3

#4

#5

I'm almost done. Did my wiring myself, and it was alot easier than I thought. My problem now, is I don't know how to wire to the spa pack. Some of the wires are loose inside and I'm not where they get connected too. I did get the spa pack company to fax me a schematic, but I still can't figure it out. I think I may take it down to one of the Spa company's and see if they can help me decipher it.