Radio Install help and suggestions please

First, order the Slingmods Radio wiring connector. It allows you to easily hookup the radio to the Slingshot wiring.
If at all possible, I'd recommend using some type of ABS or metal panel (at least 1/4" for the ABS or at least 1/8" for aluminum) to make a mounting panel. It looks like you have the PMX-8DH which measures H5.1" x W8.3" x D0.8" (130mm x 211mm x 20mm). That means you need to trim the opening for additional clearance. There isn't much room to trim because of your switches, so I'd try to see if you can gain enough clearance by removing material at the top of the opening.
Personally, I think the PMX-2 would be a lot easier to fit in the opening, using either an ABS or metal panel that you can bolt in position. The PMX-5 should also fit even though it is larger than the PMX-2 and close to the size of the opening. The unit you have is pushing the available Height and width available for the opening, but the depth of the PMX-5 might also be a problem (I think it will fit, but don't know for sure).
This thread - http://slingshotinfo.com/index…nt/38687-radiowiring-pdf/ has a PDF file that shows one of the mounting panels I made for one of my installations. I eventually used a display-less Planet Audio PGR35B round marine unit with the same overall panel dimensions I show, but a different layout for the devices I included in the panel. The most important part of the panel diagram is the dotted line surrounding the white part of the panel diagram. The dotted line represents the actual dimensions of the radio opening (roughly 7.5"W x 4.25"H, I can't remember the actual dimensions).
Good Luck. Hopefully, someone else has some better ideas than I've offered.
I just checked the Fosgate site again and I'm not sure about the PMX-5 radio because it seems top be listed as both PMX-5 and PMX-5CAN (for CANBus which may or may not introduce additional problems). Additionally, the site also refers to different models of the PMX-8 depending on how you navigate the site. Its's left me very confused, so hopefully I haven't made poor recommendations due to confusion from my reading of the site.

Quote from Trooper

@BKL thanks for the info. i was going to get the pmx-2 but after looking at them in person, i just liked the size of the pmx-8. and your also correct on the clearance. it does not need to be trimmed much. the pmx-8 comes with a plate to mount to the back side. there are 4 screws and this metal plate the pmx-8 screws to. would a dremel tool or file work better?

Since the PMX-8 comes with a backing template, by all means use it. The one thing I've noticed is that even though I'm using sheet metal screws to hold my radio/instrument panel in place, the screws still seem to want to pull through the holes/plastic threads. The backing plate will strengthen that significantly.
The Dremel will be faster while the file will probably allow you to be more precise, but much slower. I'd use the Dremel with either a fine-toothed blade or a cut-off wheel and go slow. Check carefully before you start trimming that you have enough space at the top to trim enough to install the unit w/o negatively affecting the switches. It will be a little bit of a pain, but I'd recommend making a template that reflects the outer dimensions of the head unit where it contacts the dash and an inner marking that reflects the actual dimensions you need to make the hole the head unit fits in. This can then be positioned on the dash to identify exactly where you need to trim the opening.
Since the PMX-8DH is a head unit (basically just a display w/o amplifier or actual radio) are you pairing it with the PMX-8BB?

Any success on installing these? @Trooper

Yes to pics!

Thank you!