You have to add up your amp hours. There are a lot of interactive charts on the net that can help you with that. The Bogart trimetric should be installed right away, It comes with a complicated set of instructions. But when you realize that it is just an instrument and not a control you can get the idea behind their instructions. Then the installation and programing get easier/self explanatory. There are many YouTube videos to help you with the Bogart Trimetric and the other competitive brands. Bogart seems to be the industry leader.
The reason the Trimetric is important is that it can tell you what is going on with the battery. For example, if your rig is dark/not powered up, the trimetric will show you what amps are being drawn in that condition. In a perfect situation it should only show a 1/2 amp, which covers your detectors, CO/LP etc. IF you operate your landing gear you can see what is being drawn from that activity, that might be 3 amps for 45 seconds. So right now you need to install the Trimetric even with the battery you currently have so that at least you can get an idea what your DC circuits draw. Test each DC item and jod down what it is costing in amp hours. You can be hooked up to shore power and still get an accurate reading of the DC being consumed off your charger and your OEM batt. All your interested in the beginning is how many amp hours your rig draws
When your fridge is running on LP, it uses the battery to power the circuit boards, when the water heater is on LP it uses the battery to power those circuits boards. Your inverter will give the specification as to what it consumes at idle. So add these up. This will get you going and the information you glean from that and a study of how many watts or amp hours it takes to invert 120v to run your TV and sound system including your blu-ray, a coffee pot, your wife's hair dryer and a waffle maker or your microwave. 3 minutes of microwave will pull your batts down, so if you install an inverter large enough to do that, then you use that thing sparingly. We use ours to pop popcorn sometimes or to heat a cup of water for instant coffee, but LP can heat a lot of water for what it takes to heat a cup of water in a microwave.
So all that being said, I only have 2 T1275 for a total of 300 amp hours. To preserve the life of my batts I try to only use 150 amp hours which is 50%. This is the magic number that you will hear regarding flooded lead acid batteries. It does not mean you cannot take them to 30%, but its hard on the batts and if you do it all the time battery life suffers.
I can get a charge even on cloudy days because my panels are not affected by shade over one part of the panel and they are good harvesters of light, and I have a lot of panel. I can generally replace each day what I have used plus use some of it as well. This is where your Trimetric comes in. If you see that you are at 67% then you need to not invert for the toaster waffles you wanted. Perhaps the bacon and eggs cooked with LP is a better choice. perhaps you need to turn off the home theater and watch TV with its own internal speakers and keep all the lights out. Especially if you don't know when the sun is going to shine again.
Ok now to your question, the T1275 work well for me, pay attention to the post/terminal this is important, I would use a buss bar if I did it over again and I still might. It is hard to get all those leads and monitoring wires onto the post, so one wire to the buss and then everything off the buss.
If you want only 2 to 3 12v T1275 for 450 amp hours (225 ah considering 50% discharge) then you should balance that with an adequate number of watts/amps/volts from your PVA. There is a guide for that I will send you a link.
I like the trojan batts, but there are others, continental comes to mind, There are a few others you will run across in your study. Pay attention to amp hours at the 20 hour rate. This is the only way to compare batteries for your PVA. Use the weight per ah method to see who is lying. Trojan is the name in the industrial batteries use them for a comparison, if they tell you they can get you 150 ah at 12v at the 20 hour rate for 83 lbs then that is the mark, if someone says that they can get you 150 ah for 50 lbs then someone is lying.
Currently my PVA is larger than what I need for my batts, I can get charged to 100% before noon. I can increase my capacity by adding a battery. I have 300 ah now, by adding another T1275, I will then have 450 ah, 50% of that is 225 ah.
Are you an energy hog? this is a question that must be answered, some are real frugal, some are wasters, some are middle of the road.
So the upshot is the T1275 are working good for me, my system is designed to recharge everyday but might go 3 days if extreme conservation measures are taken, i atleast get some sunshine, I'm willing to take the batts to 30 or 40%.
http://handybobsolar.wordpress.com/
http://www.amsolar.com/home/amr/page_26
http://www.batterystuff.com/kb/tools/ac-to-dc-amperage-conversion-run-through-an-inverter.html
Jim
How do the T-1275 work for you? can you go a couple days without sun?