We just got our 2002 T139 about two weeks ago and there were 2 glaringly obvious upgrades that needed to be done even before we started working on her interior. She didn't have a step/steps and the rear stabilizers were a pain in the neck to deploy and retract.
Now, I can't comment too much on the installation because my dad did pretty much all of the work aside from me handing him tools, parts, and helping him get things bolted down but if you have an angle grinder and hammer drill, you can probably figure it out.
She only had 2 rear stabilizers and only one of them functioned properly. At that, you had to pretty much crawl underneath to deploy them, it was a pain and I don't see myself doing that...EVER. After watching dad setup their 2018 Coleman with scissor stabilizers last year, I knew that was the first thing I wanted changed.
I opted for these from Amazon
These were easier to install than the steps and he used the angle grinder to cut off the old stabilizers. It took some tweaking to get them situated in the right spot (they're located more towards the back edge of the frame) but they're perfect. This came as a set of 4 so we added 2 of them to the front where there were none before and it makes a HUGE difference. This little thing feels rock solid and with drill in hand, can deploy or retract all 4 of them in about 1 minute.
This thing didn't come with any and the plastic step we had was still way too short to get in and out of the camper safely while leveled in our not nearly level driveway.
I went with this two step version from Amazon to eliminate any need to carry around that plastic step.
Dad had to do some rigging and added some angle irons to get these to slide into place but man are they nice. They feel secure and stable and I no longer feel like I'm getting in and out of a deathtrap. They fold up and tuck nicely underneath and though they hang down quite a bit, we still have about 8in+ clearance (they hang about the same height as the black water pipe). The only issue I can see with these is if we are on a spot that needs us to level out the other side of the camper, it would make the bottom step rest right on the ground but from what I hear, that side isn't usually the side that needs leveling and it's not a big deal if the step rests on the ground anyways.
All in all, very happy with both purchases and they have already been great upgrades to this almost perfect tiny camper.