How many amps does this stereo amp use per hour??

The average total power draw will be somewhere between 10 and 40ish watts.

Energy Use In The Home

GOTO Pg 3, The Executive Summary and look at the Graphs.

Speaking from experience, having worked extensively in acoustics, the average acoustic power produced will be less than 4 Watts and very likely less than 2 Watts.

EDIT: I have absolutely zero, nada, Zip experience with RVs and defer to everyone here as to the power required from the battery plus inverter system to provide that 10-40 Watts.