Sounds like a dandy choice, and if it wiorks for you, swell. My kid favours the .303 #1 Mk III S.M.L.E. I gave him for his twelvth birthday, but the #5 carbine is admittedly handy, and I have a ladyfriend who favours hers. You may find that the Sierra .303 175-grain Match King bullet gives excellent results in your .303, as it does in my own #4MkI*[T] Enfield.
I'm mostly making do with a regular full-length M16A1 and a Remington 870 behind the pickup's folding seat, and a Mauser C96 *broomhandle* pistol with detatchable holster/stock in the motorbike's saddlebag as a *substitute carbine.* Even an M1A1 with folding stock in .30 caliber is a bit too long to fit in the lockable bags, and I don't want to mount one externally. I'd prefer for one to come as a surprise, should I need to haul it out.
Like most such choices, it's a compromise, but it works for me.
-archy-/-