I do not know your tank being an 83 camper. Mine the black and gray tank appear to be a top welded to a bottom and they are ABS plastic. If yours is ABS plastic, they do plastic welding for repairs. Basically heating with a heat iron and using filler rod as needed.
They also have ABS solvent weld cement. It is used on plastic pipe fittings. Do not know if it will work as well on a flat edge of the tank. I have never used it like that. Maybe others who have used the solvent can add some more to this.
Caution on the sealants. Many plastics do not like to have glues/sealants etc stick to them. That said they do make special glues for certain plastics.
Any way to post a picture of what you have or do you know if it is ABS?
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
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