It was my understanding the only way to gain loyalty now was to do champ spawns.
So what chest are you referring to here about donations to gain town loyalty?
Is there a different chest for every town or does it just add to whatever town your already loyal to?
No there are several wayes. Depending on your playstyle or what you like to do, you can gain loyalty. Follow the link Petra gave you and all will become clear.
Example:
If your loyalty to Jhelom do
not donate in Britain. Your loyalty of Jhelom will go down and the one in Britain go up.
If you are Loyal to Jhelom donate or turn in BoDs in Jhelom. When you arrest Raiders at thier camp (NW from the road between Britain and Yew) Bring them the the guard Captain of Jhelom. The only thing you can do anywhere is the champ spawns.
A small advice, the first election will be in June. make sure the character who wants to be governor or who wants to vote are atleast adored in the town they loyal too.