I do not recommend this because it disables some safety features but.....
I use two single pole double throw automotive 40 amp relays from Auto-zone/Discount-auto/NAPA/Et-al (take your pick of vendors)
Depending on the type of slide out
The armature (moving contacts) go to the motor. one to each relay
Positive (Battetry) to the Normally Open
Negative (Chassis ground) to the normally closed.
Resting both motor leads are grounded so no operation.
The coil leads. one switch lead goes to one coil lead on each relay
The other coil lead goes to GROUND on Power gear and Positive (Battery) on Accu-Slide
You may need to "flip" the switch leads or the motor leads if it runs backward.