The IMS tanks are an excellent practical solution. Some of these do have fitment issues with petcock sealing, but those just take an hour or two of craft to sort out. In my experience they are rugged and reliable and a KLR worthy accessory.
If looks and appearance are important, the IMS plastics can difficult to deal with 'cause they don't typically take paint well. But, there are some tricks to deal with these issue.
The challenge is the porous nature of the plastics which do pass fumes (volatile solvents) through the wall of the tank and these interfere with the adhesion of either paints or even sticky backed graphics or decals.
I've seen some very clever work done with sticky graphics, where the user drilled hundreds of tiny holes in the graphic to allow fumes to pass through rather than build up and attack the adhesive.
Also, out of the box thinking required, skin the tank with custom tailored fabric, like 600d nylon in any color and pattern that your imagination can develop.
Dang ole KLR has always been a bit of a canvas to some of us.