I figured someone else might find this useful too; here are some pics of how we built our rack.
We drilled the holes using a special drillbit and screws (let me get back to you on the names for those..) We connected the two side pieces with what became the bottom shelf. We had our pieces of melamine cut at HDepot; not sure if they all will cut for you. Just take the measurements of your tubs that are on the sticker on the tub, and add an inch or two on each side (this is how we did it.)
Raw materials:
By actually placing a tub onto this shelf and putting the next shelf atop it, we got the exact space needed for that tub.
Then we just worked our way up (it is a 2-person job in my opinion; someone has to squeeze while the other person screws in the screws.)
Then eventually you have your rack!
Not sure how you want your heating; I use ExoTerra heatmats and dimmers to control them, and my hotspots stay at a nice consistent 90 degrees. Others were are muy knowledgible on Flexwatt.