Install collar beams to create a space under the ridge["false ceiling"] for air to flow from the louvered gabled end vents at the ends out the through the rafter vents and eaves[ Rob's idea].Install ample insulation over the vents in the rafter spaces and between the collar beams. If you have knee walls [or install them] insulate them.
Precisely what I did in my attic. I have construction photos at home and will post some later.
I just added one A/C vent to the train room. On the hottest days it's less than 90F up there. May seem hot, but we've run many times at the County Fair at temps well above that. With nothing but insulation, it has stayed above 50F even on the coldest days last winter. I do have a very small electric heater that easily keeps the temp above 60F.
