If at all possible avoid mounting any amps to enclosures. As soon as you mount the amp to the box the amp board and all components absorb every bit of vibration.

Pioneer Ts Wx1210a 12 Sealed Enclosure Active Subwoofer With Built In Amplifier
Mount amp to sub box. Cut out a piece of wood to mount to the box then mount the amp to that panel and use rubber grommets in between the panel and the amp. I also put a foam padding between the amp and box to protect the amp from vibration if any. The real problem with mounting an amp to a box is the box flexing if not properly made. The flex of a poorly braced box will cause the vibrations out of the box. It is very bad for the amplifier. You should properly secure the subwoofer in the trunk by using wooden plates.
I then dont tighten the screws down completly tight just enough to keep the amp in place. So for me i just love my car. Dig an 18 inch deep trench for the outdoor electrical wire which you will run from the main panel box to the garage sub panel. Meades setup is different he has very little flex from over building his enclosure. Yes you can mount a subwoofer box in the trunk by using stripes bolts multiple hinges wooden base and metallic plates. Otherwise the safest way to mount the amp to the box is to double or triple baffle the area the amp will be mounted to as well as maybe a foam board or some rubber gaskets to further reduce the vibration.
The only way to do this was to mount the amp to the box itself. It is from the flexing of the panel that the amp is mounted. You could put the box on blocksstilts and put the amp underneath the box. I know that there has been a great deal of discussion over mounting an amplifier to an enclosure and many people do it all of the time with no problems but those people probably build good enclosures from 34 or thicker mdf with extensive bracing. Do not mount amps to the sub box amplifier mounting. Use 1 14 inch pvc conduit for a 100 amp sub panel or 1 inch pvc conduit if the sub panel is 50 amps or less.
Vibration shouldnt be a huge problem unless the amp manufacturer didnt account for it when designing the solder joints. Run the conduit from the garage to the main panel box. Do not mount an amplifier on your subwoofer box. The proper way to mount an amp to a box is to get the amps mounting points as close to bracing as possible since that panel will not flex as much. I absolutely definitely love it. I dont drill the screws completly through the box.