MA Audio amp problem

Here is my issue. I recently had a stereo installed in my truck and I am having an issue with my sub amp...I am going to list everything that i have in my truck. I am running 2 sets of HK60C component sets, an HK398 amp to run my components, an HK1998 mono amp for my 2 12" MA1200XL subs. The issue that I am having is, I can turn up the radio and blast my system for a while, but the minute I turn off the truck and get back in it, my sub amp will be in protect mode and I have to wait for 15 to 20 minutes before I can use the stereo again. The sub amp is wired to 1 ohm, if this helps. My installer has changed out the sub amp twice with the same results happening. If anybody can help I would greatly appreciate it.

Sounds to me like it's getting too hot- check to see if it's got enough room to breathe.  Make sure that amp is rated for 1 ohm operation.  Also ensure the gain is set properly.My ex once told me I have a perfect face for radio.

If mounted underneath an seat invertedly the amp is not getting sufficient air to cool properly...Try mounting it somewhere where there's more air or build a custom amp rack for it.

By inverted you mean upside down. If so check and see if the amp is rated to be mounted like this,  most amps are not. It can cause the amp to heat up and eventually kill it. Try mounting the amp with heat sinks up or close to, also in a spot with more airflow or get a fan to cool it down.

Thanks guys for the info, I just figured as did my installer that the amps would be okay to be mounted in that position since it is wide open under the seats. I can't seem to find any other place to mount the amps but where they are at.