Compass prams


could I please have assistance with compass prams

I have a high metal rover and would like to know what param I can adjust to realign to mag north. the auto decline works well after a few driven circles but if rover is stationary too long it will loose true orientation.

next issue GPS only navigation if I turn of all compass and disable param Compass_use so GPS is use for heading the mode will fail to change

The only suggestion I have is to use a long GPS pole and use a GPS with external mag.