Nothing is REALLY wrong with putting it under the seat. I like to put my amps somewhere where they won't have cooling issues. Mind you, I broke 2 alternators in the 200B last time I had my last set of subs installed.
Im going to be mounting them in the boot, similar to that picture on the previous page. That way they are easily reachable, you can adjust settings by opening the boot and there's plenty of space for cooling. Mind you, these are the cheaper end of amps, if you're getting a flash one you can have remote adjusters.
It also comes down to how pretty your amps are as well. Many show cars put them out in the open to tweak for shows, and to show the cool designs they may/may not display. But I suppose you're not trying to win a fashion show in the 200B?
good luck