Are we talking on leather seats/trim or fabric seats or plastic trim?
On fabric, depending on the type of sun tan lotion, it will stain/dye/discolor the fabric that is impossible to remove because the fabric absorbs lotion and, depending on how long it has been there, it becomes a permanent part of the fabric structure. Lotions with orange scents or those with tanning color-enhancers are the worst. While your skin can eventually slough (AKA grow and then die or flake off) off this coloration, fabric does not. Light colored fabrics/clothes will show this discoloration the most, obviously. Short of a re-dye of a fabric, I doubt that this can be removed or remedied.
I am sure that someone might mention a steam-cleaner.
If you have oils from the suntan lotion to remove on fabric, I suggest WD-40`s Spot Shot Stain Remover that you can find at Walmart. I found it good in tar, BUT if the oil or tar is left on for too long, the petroleum will discolor the fabric a yellow tinge. This product is like a "denatured WD-40" without the fish-oil scent that has been developed for clothes and fabrics. I used to use regular WD-40 (the shop spray lubricant) for cleaning fabric/carpet floor mats that got tar/blacktop sealant on them to dissolve it, but the fish-oil smell was over-powering and would linger for several days, even with necessary subsequent carpet shampoo. Spot Shot does not have that problem. I DO think, at least in my experience, that regular WD-40 is a better solvent/cleaner than Spot Shot for oil and tar, though.
I have since migrated to Optimum Polymer Technologies Carpet and Fabric Cleaner and it gets about 90% of most stains out on fabrics. I still pre-treat some stains with various stain pre-treaters OR just dab a small amount of full-strength Optimum Power Clean on the stain. I do NOT use diluted (3:1) Power Clean for fabric or carpet cleaning, as the smell is just too "industrial" and solvent-like and it lingers for WEEKS, not days when absorbed by the fabric material, and it will not rinse out. The OPT Carpet and Fabric cleaner has a very pleasant, antiseptic-clean smell that seems to kill odors and it cleans very well, which is why I like it for fabric material. Power Clean is a great cleaner/degreaser for hard surfaces, like paint, metal, or plastics.
So when you say door panels, I am assuming that these are plastic, but they may have fabric or leather insets in them, depending on they type and make of your vehicle.