Dual Battery Wiring and Fuse questions

I have been doing a lot of reading on installing a dual/aux battery system in my 09 tacoma. i think that i have read every thread on every forum there is. i have decided on a hellroaring isolator with a optima 34/78. my problem is that i am not sure what size wire and fuse to use. The Hellroaring folks told me to use 8 awg with 50 amp circuit breakers. Based on my estimated continuous use of 15-20 amps. from all i have read this doesnt seem to be enough. The Perfect Switch solid state relay recommends a 150amp fuse. A number of the solenoid based isolators are recommending somewhere around 100amp or higher fuses and appropriate wire.

Is it the difference between the solid state relay and the isolater that causes this difference?

Or perhaps because i am not running a winch i dont need the bigger rated wire.

Or is it more that the hellroaring isolator (95150B) isnt rated for that many amps? (75 continuous and 250 spike these are the numbers that i could find but they were for an older model)

any thoughts would be much appreciated