Cooper-I think you will have a better chance of getting the air out if you have the tire lying down perfectly flat and level. I will show you a few pictures of what I did and maybe it will help you decide.
I used large vents but it still had air trapped but I think getting it filled just barely to the top would help let the air out easier. But the bad side of that is if it is not full the tire will be no good.
The nubs are easily trimmed off and sanded smooth.
Also be sure of the hardness you need. I thought this was good but with an extreme load on the truck there was no flex in the tire. I can send you more pictures if you want.