I bought an extended cab Ranger new back in 04- 4L SOHC, 5 speed FX4 package. 3 years later, I sold it to my dad, and he's driven it since. It has been well cared for since the day it was driven off of the lot, and it has been garage kept.
The truck has somewhere around 110,000 miles on it now. Dad has had problems with the fuel sending unit, plus a check engine light that was temp related. So, the plan was to pull the bed and replace the sending unit/pump, put a new fuel filter on it while the pressure was bled off, and put in a new thermostat. All the work went without a hitch, other than finding horrible rust in the bed.
Some of the cross supports were rusted heavy, but no major deterioration, yet. At the head of the bed, though, where it hangs down just below the bottom of the rear cab, it was all eaten away. We wire brushed it real well, coated it with two coats of rust inhibitor, and painted the snot out of it. The rust isn't into the bed floor- it looks like the cab protects it, and what is gone is because of what the front tires throw back.
My 18 year old daughter has a 98- same truck except no OHC, and it's an auto- and the head of her bed looks fine. I do plan to pull the bed before Winter sets in, and check everything out underneath. It will be time well spent- this road brine that is used now in VA is nasty stuff.
By the way, we have now owned 5 Rangers- they are a great value.

 

Interesting that you should bring up the subject of rust. I started to work my 01 ranger rust issues a couple weeks ago, mainly around the mud flaps. Crawling around under the fenders I noticed the same rust issues at the front of the bed. I don't have the guts to remove the bed so I scraped as much potato chip sized pieces of rust off as I could and sprayed it well with that rubberized stuff. Also sprayed the inside front of the bed where the seams and torque screws are.
You make it sound like removing the bed is "a piece of cake".
Back to the mud flaps:
The mud flaps are in my trash barrel. They are one of the biggest rust contributors that I see on my Ranger. Thanks to 3M's abrasive rotary tool, Bondo and thick primer I've got them cleaned up fairly well. Also sprayed all around the inside of the fenders with that rubberized stuff.
I'm using Dupli-Color Perfect Match Touch-up Paint and Clear Coat to apply the finishing touches.
It's not a Perfect Match, but it's good enough.
I will do some more undercoat spraying when finished with the painting.
Bob P.

 

It's interesting that I haven't found the same rust in the 98.
Pulling the bed off isn't bad at all, if; 1) you can get to the bed bolts. I would imagine that a commercially sprayed bedliner makes it harder, since the bolts are typically sprayed over, and 2) if the bolts will come out. This is the third Ranger bed that I've pulled, and it takes 20-30 minutes, at the most, if the bolts come out cleanly. I always apply antiseize when putting them back, so the next time will be a piece of cake.
The things involved- 6 bed bolts to remove, one harness to unclick the connector, and take the filler neck loose. Then, get a buddy or two, and lift the bed off. I also pull the tailgate to lighten the bed and make life simpler.