I will chime in and try to keep things simple.
I have a 2015 Hawk (started camping in it 4/16/15) after installing two Optima Blue Top Deep Cycle AGMs. They are still in the camper and performing at about 90% efficiency compared to new. Not half bad for 41 month old batteries.
But, the key is maintaining deep cycle batteries at peak storage capacity to the greatest extent possible. Obviously, they are meant to be deeply discharged. But, they must be fully charged as soon as possible when they are drained into a deep discharge condition. Failing to do so will greatly decrease the longevity of the batteries.
Vic hit upon a very important important variable. Charging with the vehicle's alternator. The "hot" wire comes off the positive of the crank battery and should be a gauge suitable to carry the suitable amperage to the camper batteries; gauge will be dependent upon the length of the run.
Also, toss out the 2015 FWC battery separator (can't even recall the brand name anymore) and install the Blue Seas ML-ACR Automatic Charging Relay with Manual Control -12V DC. This will allow you to override the relay and charge your camper batteries with the truck when camper batteries are in a deep discharge. You must use the manual override judiciously as this places a very heavy load on the crank battery.
If you are living in the camper full time, I suspect you are putting a heavy drain on the camper batteries and they are not getting a full recharge before the next deep discharge. The deeper the discharge and the longer the period before a full recharge, can reduce the life span of expensive AGM deep cycle batteries to mere months. Further, a partial recharge and then a deep discharge is hard on deep cycle batteries and will reduce life span as well. I learned this expensive lessen the hard way on my flats fishing boat that had a 24v trolling motor.
In-so-far as solar charging. You only get 100% efficiency from the panel when it is exactly 90' to the sun. Any "angle off" will diminish solar gain and charging efficiency. More then 30' angle off will greatly reduce the panel's charging efficiency.
Further, shading of a single cell (say 1 of 36 cells) can reduce the entire panel charging efficiency by as much as 75%. I didn't install racks of on my camper roof for this very reason, I can't accept shade on the solar panel. I'm also keenly aware of the sun's relationship to the panel with the roof vent open so I don't needlessly shade a cell. An important aspect camping days on end in the same spot out in the desert. And, I use a portable panel. I would submit the portable panel is far more efficient than the fixed roof mounted panel as long as you keep the panel oriented towards the sun throughout the day.
To get the most out of solar charging, one should learn the nuances of the system, its limitations and techniques to gain the most from a solar charging system. There is some really good info online as it relates to campers and RVs. While there are some really nice controllers on the market that let you know charging and discharge rates along with a host of other variables, nothing beats using good techniques to conserving the energy in your batteries. And really, that's what we're talking about energy conservation and using good techniques as they relate to your solar charging system thereby reducing the burden on the system itself.
Good luck.
Edited by Advmoto18, 11 September 2018 - 09:55 PM.