Spray foam is not a good idea. Those hatches are probably there to allow access to some equipment
or fixings. If you spray foam it it will be a impossible to access these things.
Get some double sides tape and those soft jigsaw like playmats for children
if you want to save money
or something like Armaflex. Tape all the joints so moisture doesnt get into between the seams to the cold hull
to form condensation
Shade your windows first to see if that. A lot of heat is coming through those.