The cabinets that you linked to look like they're solidly built but I honestly question the use of a bedliner as a coating... Most amp cab companies use a simliar resin/mesh material, often Tolex, but this is much thinner and it actually hardens into a more vibration-friendly material... From what I know of bedliner material... it never fully cures into a hard material but maintains a slight rubbery feel... this is terrible for resonance. I can understand if the idea of the cab is to let the speakers and amp do the talking... but part of a well designed cabinet is the fact that it compliments and helps project the sound of the speakers and amp.
Which leads me to another point - Be sure you get quality speakers in the cab that you choose. A great amp can be ruined by poorly balanced speakers...
Just a few points to take note of while you're looking around. Usually, just avoid plywood and you should be good to go...