Buy a little at a time. To cut your monthly expenses, spread your RV purchases over a period of time. Buy part of what you need today and the rest next month when you have more money. This way you can get what you need and yet not break your budget doing it. You can stay within your budget and stay out of debt for you incidental RV purchases.
I am buying the hook up system for my towed vehicle a bit at a time. I purchase the brake system first. I will watch the sales and purchase my tow bar and the bracket or base plate that goes on the toad next. Obviously I can not tow my vehicle until it is all in place, but for right now I do not have any trips planned that I will need the toad to come along.
I hate having things put on a credit card. You have the items today, but you pay outrageous interest rates for that privilege if you do not pay off the card each month. I like the idea of buying what I can afford today and the rest tomorrow.
I did the front brakes on the motorhome myself. There was enough pad left that I decided to wait a couple months to do the rear brakes. Again, I am spreading my expenses out over time.
Everything you put in your RV can be purchased over a period of time. You can take dishes and silverware from home until you can afford or find just the right ones for you.
You can buy a cheap pop up awning until you are ready to buy the pull down awning that attaches to the side of your RV. We got one of those 10x10 foot easy up awnings for $68 on sale. It goes up fast and works great. I will get the "real thing" later.
Are there any projects you want to do on your RV. Maybe re-caulk the roof before it leaks. Buy your Eternabond tape now and have it on hand for the project. Do you want a computer work station? Plan it, then watch for the right desk and other materials you will need. Get it a piece at a time.
Do not get caught up in the "have to have it now" trap. It will run up credit card bills and expenses a lot more than waiting. Of course many RVers can go out and get everything today. That is what we all would like to be able to do. Since many of us can not do this, this technique of a little at a time will still give you wonderful times in your RV and still keep you within your budget.