I cannot help on the exterior LED but I did do the inside ones starting back in 2009. This thread was started back then an I joined in half way through with my upgrade. This may help, you can scroll before and after this reply in that post
We have now converted the entire inside of the camper to LED's. Back then the cost was a large factor at $15 a bulb but it was worth it from the lower power draw when boondocking. It took us across 3 years to change them all out to spread out the cost but it was well worth it and yes, polarity is a need. I think I had to swap maybe 1 or 2 fixtures wires to get them all to work.
Quality, back in 2009 this was a big deal as the LED's where just comeing on the scene. The ones from Super Bright where good quality and I have not had any issues with mine since 2009. Others have reported poor quality on other cheaper E bay sites. But again, technology has advanced a lot since then so it may be better now. If they are dirt cheap, there may be a reason. I have had home LED bulbs die in the 1st year bought a year ago so but they are much bigger bulbs.
A few pointers, figure out if you like warm white or cool white. Warm white is closer to the look of the prior incandescents. Cool white is better for reading but can be too white for the entire camper sometimes. We use the warm white in 90% of the camper but the 2 lights the wife reads by.
Pending the age of your camper the plug in base can be different as the fixtures changed. We went to Super Bright LED's web site and bought from them. https://www.superbrightleds.com/
You have to drill down into the selection which is close to endless. They now have an RV section. Amazon and other sire now have a lot to offer but Super Bright LEDs is still good.
This flat wedge base fits most of ours. https://www.superbrightleds.com/more...ofit-rvb/2805/
And with technology cost is now 3 times less and they are up to 130 lumens in the same size. Our first ones where more like 105 lumens. The 130 for sure would be better and much below 100 lumens for a general area light is not the greatest.
I think Mainah has plowed the ground on the DOT lights and converted them. He also has an older camper and they may be closer to your 89 camper. He will know what he found that worked.
Ideally you have time to do the conversion, but a few styles to try, try them and make sure you like them and then buy more of the "right" ones.
Hope this helps
Please post what DOT lights you find work. We have had a lot of talk on these but not many have posted the brand and where they got them. Inside lights we have much on. Try doing a Google Custom search on our forum. Lots to read. Use this link, https://cse.google.com/cse/home?cx=0...95:95x3m3w6lto
Enter "LED lights" in the lower Google Custom search box and hit go. You can read for a good while but look at the dates, while good info some may be from the 2008 and 2009 time when LED just started out. Newer better things may have come since.
Current Sunlines: 2004 T310SR, 2004 T1950, 2004 T2475, 2007 T2499, 2004 T317SR
Prior Sunlines: 2004 T2499 - Fern Blue
2005 Ford F350 Lariat, 6.8L V10 W/ 4.10 rear axle, CC, Short Bed, SRW. Reese HP trunnion bar hitch W/ HP DC
Google Custom Search For Sunline Owners Club