Good call with the spacers and vertical mount. If the fan doesn't help I'll add those. With my calibrated hand it had quite a bit of air moving over the heat sinks. Impeadance is OK with my setup, but I didn't start having problems until 3 unique events happened:
1. Wife packed so much #@$! in there that it couldn't get any air. I took care of that problem
2. Got hot out. Happened on the first 90+ deg day. Had 40 hours on the setup (spring/early summer riding) before any issues popped up.
3. Didn't have any kids on the boat, and no one else around, so we cranked the DBots while we were riding. Sounded very good BTW until the amp shut down.