When I was mounting my own stuff, it's been a few years I used laquer thinner and 3M Contact Cement. You'lou'll also need a tire horn and some sort of pan. I used to use a med pyrex backing dish for this.
1. Coat foam donughts with contact cement on the inside
2. Coat wheels with contact cement
3. Let these set-up for a few minutes.
4. Pour laquer thinner into your dish, 1/4" should be enough
5. Place wheel into laquer thinner getting the contact cement wet.
6. Place horn over rim
7. Roll your foam donught thru the laquer thinner, you want to get the inside a little wet.
8. Slide over horn onto the rim. The laquer thinner keeps everything wet so that the contact cement doesn't adhere before you get the donught over the rim.
9. Let them dry and true.

I used to do a whole seasons worth of 1/12 tires in a night. Usually 8-10 pairs each front and rears. Used to take a couple of hours to mount them.