It has been a while since I bought motorhome tires, so will yield to others on that one, but have had good results with the Goodyear G670. I am not a fan of RV covers unless you mean a roof over the RV pad. The cloth covers are a chore to put on and take off and if you have a lot of wind they can rub places on the RV.
On batteries, the number you need just depends on how you use it. You probably have two 6V batteries now and you need 2 in series to get 12V. If you travel like we do and rarely stay more than one night in a place with no shore power, the 2 batteries will serve you just fine but if you plan to spend a lot of time camping where you do not have shore power, then 4 batteries would be a very good upgrade, especially if you will be in places that require use of the furnace. Solar is by far the best answer for those who are true boondockers and spend lots of time where there are no power connections. For people like us who rarely are without shore power it would be a waste of money.