Strain relief / knockout fittings

[powerscol]

Good morning everyone.

I am gathering parts for my solar/inverter upgrade. My transfer switch is housed in a very sturdy plastic box with knockouts all around ranging from 1/2", 3/4" , 1"and 1.5 inch. I cant use the 1.5 ones as there is not enough clearance inside to clear the switch. The back of the Go Power 3000w inverter that I plan to use has the typical clamp type connection. It is not dust or moisture resistant. At this point I am not planning on running flexible conduit to contain the wires. If I do I can use the water tight connections made for conduit installs and problem is solved, but that is a whole lot of extra work and cover only one of the 4 connections to the switch needed

I would like something that is dust proof and hopefully water resistant. I have found cable gland clamps, water tight fittings for flexible plastic conduit (I would silicone any void) but they don't offer any strain relief. I can just use the old school clamps like is on the back of the inverter https://gpelectric.com/products/3000...wave-inverter/ and fill in any void. I really don't like the clamp type as they can damage the cable/wire sheathing , especially with vibration.

So what have you folks used that works?
Thanks for any thoughts or ideas.