Look for a foam store in your area. Up here we have a foam place and we redid all of the foam in our old TT.
You can pick thickness and density of the foam and get it cut to whatever size you need. Finding somewhere to put it while the dinette is set up could be fun though.
2014 Jayco Swift 281BHS
2015 F250 XLT 4x4 Crew Cab, Short box, 6.2 gas
Solar powered! The trailer not the truck!