you got a good point because sometimes a prefab can be good but i saw a prefab my brother had for his solobaric l7 15 and it was like 2 cubes tuned to around 38 Hz with 11 inches of port per cube and all the sides besides the front baffle were 1/2" particle board.
that ended the chance of every using a prefab for me
Yeah that's why people tend to dislike them so much. Some small shop don't care about their customers, all they care about is profit so they get the cheapest prefabs they can. I went to a shop once to ask for a box for my cousin (he has 2 L7 12s at the time) and the shop guy pointed at some prefabs he had against his wall. I told him I thought it would need to be a custom box and he said no that those would work. I told him no because the L7s were square and he only had round speaker openings and his answer was, I can just cut the squares around the circles so they can fit. So that showed that some shops don't even care about their customers, since he couldn't even order a prefab box for the subs we had.
But if you look online there are some decent prefabs, I heard Q-Logic builds some pretty good ones.