Edit: Its been a year since I last played, looks like 1.0 saw an overhaul to raid mechanics.

~~From what I recall, raids are scaled. Don't recall what they scale off. Possibly based on the highest level of players within a guild, or maybe of pals within a base.~~

If you are running a standalone server, there is a server config file with a fair amount of options, might be able to tweak some settings there for damage.

One setting I do know exists is you can turn off the slow damage over time to structures built outside of a bases radius, increase the number of pals a base can support, the number of bases that can be made.

Not sure what options you can set if just hosting a game and inviting people.

A common strategy to mostly eliminate raids, at least when I last played, was to build bases in a few specific locations that were either impossible, or difficult for the attackers to path to, but means location options are a bit limited as there are only a handful of good building spots like that.