There’s a big advantage with bent foam rather than kerfed … the kerfing leaves only a small bit of original material on the outside of the bend …that is unless the kerfs are cut exact according to formula and then all glued solid ( the math) … The heat bent foam is One piece solid all the way through , and when cooled the foam STAYS in that shape , no stresses , no springback … That and the rolled shape makes it very strong
Obviously a heat blanket or hot water tank would be a good heat source , and building forms to bend around gives you an exact shape , but those things are only really good for production run of foamie trailers , not really practical for just one trailer … But if we put our heads together I’m sure we can all come up with a simple practical way for “home garage” use …
Now as far as the bending , the only surfaces you really have to heat is the inner and outer surfaces… the inside core is pretty neutral and will follow the outsides which stretch ( tension on the outer curve) and compress ( the inner surface of the curve) . How do I know this … I’ve been heat bending thinner foams for years now , very successfully … Just need to bump it up to a bigger scale … Remember
you don’t want any heat hotter than boiling water or you’ll melt the surfaces ( not good ) …
For you folks living out west , just put the foam in the Sun , that should get it soft enough to bend slowly ...
Been a HOT summer already …!!!