I was planning to put a tilt ability for the panels on the van's roof. What is the difference between the Voc and the Vmp? As for the max Voc potential, you're saying I shouldn't put all 3 in series, but only 2, leaving one in parallel to avoid any potential overage on the MPPT which is limited to 115v... correct?
Correct regarding only 2 in series. Avoid having Voc exceed top end of charge controller's MPPT range or it may not start operating. Definitely avoid exceeding maximum voltage spec to prevent damage.
But, don't do 2 in series, paralleled with 1. That'll pull down the 2 series string to about Voc of the 1, and force excessive current into the 1. You should use 4 panels in 2s2p configuration. Or 3 panels 1s3p if voltage would still be high enough. Or use a different charge controller with high enough voltage ratings for 3s1p.
I have suggested an MC-4 "Y" cable with fuses as an alternative to combiner box, but two many strings could exceed current capability of the wire. I've seen 4 or 5 input "Y" cables. Some panels are 4 amp and others are 7 amp. 7 x 4 = 28A is a bit too much for either a 10 AWG wire unfused or for a 30A fuse suitable for that wire. Fuses should be at least 25% higher than the peak PV Isc under all temperature and illumination conditions. I forget just how much oversize a wire should be to use unfused, probably at least 50%.
Voc, shown on the label and data sheet, is the voltage you would see with a volt meter on the wires, with open circuit (no current being drawn), panel at 25 degrees C, illumination of one standard sun (1000 W/m^2 and the spectrum we get from sun directly overhead.)
Your actual Volts Open Circuit could be higher on a cold day, or with direct sun on the panel plus light bouncing off nearby clouds.
Isc is the short circuit current you get with an ammeter across the leads (voltage pulled to zero by the meter) and same temperature and illumination conditions.
Your actual current short circuit could be higher, so don't want to use too small a fuse, and if no fuse the wires need to be suitably oversized.
Vmp and Imp are the particular voltage and current with a load ideally sized such that power = Vmp x Imp are maximum. Again under standard temperature and illumination.
Your actual power will typically be lower because panels get warmed in the sun. Sometimes higher on a cold day. The label specs are "STC" for standard test conditions. You may also see specs for "PTC", which are realistic performance test conditions of elevated temperature and a slight breeze that carries heat away.
This link suggests PTC could be 10% to 15% less than STC:
Are you comparing solar panel options? Efficiency — the panels’ ability to convert sunlight into energy — is a feature you should consider.
www.intermtnwindandsolar.com
You also have losses due to wiring IR drop and inverter efficiency. I had a system with Sharp polycrystaline panels that appear to have delivered AC power 84% of PTC ratings, and that with an inverter in the 92% to 95% range. Another with Astropower monocrystaline only performed that well initially, then dropped to about 70% of PTC.