James,
I have a Jensen 400 watt, 4 channel amp under mine and it works fine.   It
can get a little warm if you are really cranking up your music, but at
normal listening levels (this may vary depending on how loud you like your
music) it's fine.  Actually, I put in a 400 watt for two reasons:
1) I like good, clean sound at (sometimes) high volume levels
2) A higher watt amp has to work less (which means less heat) to produce
normal levels of volume

You can see my set up at:

http://home.earthlink.net/~matsuwesty/page49.html

Hope this helps.
Matt

I have a 150x2 watt amp (no built-in fan) that I'd like to locate under the
driver seat to save space elsewhere and to simplify installation (will power
front speakers only). I know this location isn't generally recommended on
passenger cars because of limited air flow, but I know some have done it in
their Vanagons.

Has anyone had any problems with this set up?

Does it generate noticeable (annoying) heat when your sitting?

There is about a 1.5" gap along the front edge of that under-seat
compartment. Would adding a small DC accessory fan there be effective in
cooling (there isn't an opening at the other end)?

Thanks,

James V
90 Carat