If radio works independant from iginition on a direct feed via inline or fuse box fuse then you could have a faulty radio on / off switch draining the battery as with most if not all, the on/off switch is also the volume switch.
Try removing the radio fuse to disconnect the radio then re-charge the motorhome battery then see how it performs with radio out of action, if ok then you've found your fault. If no different with starting .....knackered battery get it tested. IF Battery tests ok then look at starter problem alternative is call in Auto Electrician.
bob, January 2010