As greyghost mentioned stirrups should be sent longenough so that you can just take the weight off your butt.
Keep your toes pointed up and out. The best boots are 'packers'. Shove 'em in the stirrup clear to the instep/arch. The heal keeps the boot from going through the stirrup. But never the less, whatever kind of footwear, toes up and out.
Ride the horse, just don't sit there like a bump on a stump. It makes your butt and knees sore and ticks off the horse.
With your toes up and out your knees won't get sore but you'll walk a bit bow legged and kind of waddle a bit for a while leaving funny tracks in the snow.
Also it helps if the stirrups are a bit to the front but that's not too big a deal.
13 miles isn't that long, maybe a couple of hours. You'll do us proud.
oh yea, BTW, leave the spurs @ home
ANd good huntin'