Asphalt will likely fail under such a heavy vehicle. Normal driveways in my area are typically 4" thick asphalt over 6" of compacted stone... and they are designed to handle the weight of a 5000-7000 lbs vehicle. 8000 lbs axles is a LOT of weight in a small area. Asphalt takes a year to completely cure, and they recommend that you don't park in the same spot for long periods of time until it cures. I think you will be greatly disappointed with asphalt.
If you want asphalt to tie in to your existing driveway, I would strongly encourage you to prep and pour concrete pads for your axles and front jacks, then get asphalt laid around those pads and tie it in to the rest of the driveway.
If not, I would have a MUCH thicker base of gravel, and make sure they install the gravel in 2-3" lifts and thoroughly compact the gravel between lifts. An asphalt driveway is only as good as the foundation. If/when the foundation settles, the asphalt will settle, causing potholes or ruts.