minnesotsamoddeler purposes vacuum cleaner boxes by cutting and refolding them. The boxes are almost as nice as the models.
'strue, if you want to take the time to do it you can use just about any old long box (refrigerator boxes are usually easy to beg off of appliance stores, if you have a big enough vehicle). Use a long straight edge and a utility knife to cut 'em out, "score" where you want to fold using something blunt (about 1/8" radius is good) -- you want to crush the cardboard, not cut it, fold over the edge of a long table.
I used to work in the shipping room of my dad's manufacturing business; I couldn't count how many boxes I made or modified.