Coast Aluminum had useable stuff. They have multiple store nationwide for anyone curious.
I got 60" by 144" {5' x 12'} sheets for $80 per when you buy over 3 which I bought 4 and will called them.
My 31'
Sovereign uses an 11' long front piece in front of the water tank box and about a 6-7' piece behind the water tank box so that is 1-1/2 sheets. Then I will cut the other 2 sheets down to 2.5' wide {30"} and use those and the side rolling pan piece. The 60" wide center piece will sit right on my frame rails and be riveted to the cross members, the side wrap pieces will fit up under the side wall and rivet to the C-Channel and wrap under and over lap the frame rail and center sheet to seal over the center piece.
Plenty of support, plenty of lap for riveting and sealing.
They only sell roll coil aluminum by the full roll...so that did not work, but the 5x12 sheets are fine. They are 3003 and I think T-3 heat treatment.
The thinnest they had was 0.040" which is fine...a bit thick but not that much heavier to cause stress to me.
I do not think they list the 60" x 144" in 0.040" on their website but they had it in stock here in the Santa Fe springs plant. I will called the same day I called.
$345 for 4 sheets which will make all of the bottom and side wraps {other than the banana wraps of course} and have some spare of maybe 5' x 5' for a rear patch I need is not too bad in my book...
Hope that helps others.