Well, your signature confused me with a different type of MH you are asking about.
The coolant for a Cummings should be fleetguard, you can use the "complete" version, which has the antifreeze and distilled water mixed in the proper ratio, plus the coolant additive to prevent cavitation. Or you can purchase the antifreeze only, and add distilled water so you have about a 50/50 or 60/40 mix depending on where you live and how cold it gets.
Looking at the back of the engine, assuming you have a lift up door, on the left side of the engine compartment, there should be a tank, which has a radiator cap on it, halfway down should be a sight gauge, it is not that dependable, because coolant hangs in the space the sight gauge is screwed into. However, if the engine is warmed to operating temp, and coolant is showing in the gauge it should be ok. Cummings recommends the coolant be flushed out and replaced and new additive and coolant added at 50K miles I think, you can call any Cummings shop and they will tell you. I would check the coolant with the engine cold, by removing the radiator cap and using an inspection mirror and flashlight, see what the level in the tank is. The Cummings engine manual should also list the type of coolant used in the model of engine you have. If you don't have one, it can be ordered from Cummings.
If you have not had the coolant additive ratio checked in a while, it would be prudent to run it to a Cummings shop and have them check it and add the additive as necessary. I usually have them change the oil, filter, and doing the coolant check is easy at that time. Once I get the shop built, and I can figure out how big a collection pan I need, I will do my own filter and oil change. I do those once a year, regardless of mileage. I will do the fuel filter myself every other year. I drain the water separator portion about every two months because we just don't use our coach much as far as mileage goes.
Monty & Janet - 2007 Alpine APEX 40 MDTS
S/N - 75715 - Retired - Master Certified RV Tech