Hey zvizdic,
Some interesting ideas here..however you may be trying to solve a problem that you don't have?
When we dig deeper into the workings of these PWM controllers they will reveal that changing the amount of load they have hooked to them does not change the amount dumped. WHAT??
If we have a dump load of 1000 watts at our set point voltage and the battery bank is receiving 500 watts too much, the controller will PWM an equivalent of 500 watts to the dump...it will be running at a 50% duty cycle.
If we have a dump load of 2000 watts at our set point voltage and the battery bank is receiving 500 watts too much, the controller will PWM an equivalent of 500 watts to the dump....it will be running at a 25% duty cycle.
If we are looking to move the dump heat inside the house in the winter from a battery some distance away you could do the ghurd controller->
timer board->inverter->AC heater method?
Fun stuff, dave
Edited to add: of course we always need to have at least enough to dump our maximum charging abilities plus headroom...the dump load size is then limited to the controller/component ratings.