Myr332, I've got 2 amps in my R33, one of which is sitting to the right of the battery, on top of the fuel pump. In the 2nd pic that fhrx posted, what I did is mount my amp to a small piece of mdf, then using wingnuts and washers, mount the mdf onto the bottom of the metal bracket (that holds the battery and whatnot). All I did then is put some soft foam underneath for extra support, not that you really need it.
The pic attached shows where the 2nd amp went.