building custom boxes

i'm thinking about building a cust box or enclosure for my subz. how hard is this and what kind of materials would i need.

it's either build a box or build a side panel to mount my amps and cap. how can i mount my sub box so it doesn't slide around everywhere?

L brackets work well, but dont look nice

how hard is it to build a total custom enclosure

i saw these guys build one in the back of their 97 accord and they were able to mount the subs flush with the the floor. it looked pretty ill.