If you go HERE
you can download manuals for many of the items in your coach like the water heater, furnace, etc.
I don't know about 93 model years but in later years - like after 1994 - or maybe earlier - it is common for parasitic loads to discharge the engine battery in as little as two weeks or so. This is due to keep alive currents required by engine computers, radios, step lights and so forth.
When connected to shore power the house batteries are charged by a converter that puts out 13.5 volts dc.
That output also supplies everything in the coach that requires dc voltage. Examples are the control boards in the refrigerator, furnace, water heater,and air conditioner.
The house batteries are also charged by the alternator when the engine is running.
In some motor homes the engine battery is also charged by a B.I.R.D. system when you are connected to shore power but I think most are not.
The house batteries should be deep cycle types.
Popular brands are Trojan, and Interstate.
Sometimes they are two 6 volt units wired to series to give 12 volts. Often golf cart batteries are used in that case. Many people get them from Cosco or Sam's Club.
They may also be two 12 volt batteries wired in parallel or just one 12 volt battery.
There is often a Disconnect Switch often located on a wall close to the steps that disconnects the house batteries when it is stored. I haven't seen one but there are also disconnect switches for engine batteries . I believe they usually on the dash.
There is usually a momentary AUX Switch on the dash that temporarily connects the engine battery to the house batteries for emergency starting.