I can't speak for the little folding portables but I would imagine they are just as sturdy as my big panels that are 40x65 and ride face to face with a blanket in between either standing in the walkway, on the bed or strapped to the rack on the truck.
The largest folding portable I can find is a 200w but it is $500. You could get the same without the hinges and legs for $300. ( I use pine slates and c-clamps) I am pretty sure folded it is 21x47x3.
clickThis is a page of 200w kits without the hinges.
clickThere are other options like Uni-solar rolls and thin panels too.
