Tapping switches power source

Thinking of installing a fuse block, such as the Denali powerblock2, or similar (open to suggestions).

As the unit needs to tap a switched power source to relay/coordinate same to accessories powered off the block, what/where would you recommend tapping into from your experience?

Any tips on waterproof splices? Can plasticoat it, sure; anything else?

Depends on where you locate the block. Mine is under the left or right panel under/beside saddle.
One side is switched 12v fuseblock and the other side is constant 12v. Can't remember which side is which.
Anyway it is imperative the block is powered direct from the battery but is switched on by relay from the switched source.
I used the tail light connector beside the saddle. Pulled out the live pin from the connector, recrimped it with my switch wire to the auxiliary fuse block, and reinserted pin back into connector.
Don't like wire taps. All my connectors pins etc where wires are bare, are doused in Vaseline for moisture protection.