I second the JB Weld suggestion - they have a
fiberglass epoxy putty stick available at Home Depot that mixes super-hard. I used that to fill in the holes from the old lights and replaced with Peterson (I wasn't happy with the quality of the Grote brand, so I sent those back). I found some on Amazon and some on various online RV parts stores - it pays to shop around because some of the lights were under $4 at one retailer and were $11 at another - makes a difference when you are replacing them all! The round ones are called clearance lights (my
Bigfoot had both yellow and red clearance lights). Look at the number on the original fixtures and search for that on each website to get the correct replacement.
I caution on buying LED light fixtures and recommend going with incandescent fixtures and then replacing the bulbs with LED. I found that many of the LED fixtures are sealed so you cannot replace the bulb when it goes out, but have to replace the entire light fixture. Also, when I was shopping for taillights, I found a great price on a set of LED taillights only to find that once installed, they were not even visible during the day - not at all - so I had to purchase some Bargman incandescent taillights and then replace the bulbs with bright LEDs instead. Worked much better.
Make sure you are getting surface mounted not recessed (it's sometimes hard to tell from the photos online, but the description should say surface mount).
Here are some examples of where to find them (again, check what your old model # is to find best replacement for your needs):
https://www.finditparts.com/products...lighting-m102r
https://www.amazon.com/Peterson-Manu.../dp/B000DN7P5M
In attaching the new lights, I also used waterproof heatshrink connectors to ensure that the wiring would never corrode. Harbor Freight sells them cheap!
Happy renovating!