The rust situation on my '84 244 was far more progressed than yours. I've used POR 15 for years and overall have been satisfied with the results. Just make sure that you follow the directions to the letter, and clean, clean, clean the rusted surfaces before applying the product.

To patch larger holes, I used fresh sheets of aluminum and riveted them in place, then used a POR-15 seam sealant, then covered the lot with a POR-15 undercoating.

I've spent many hours on my back fixing rust on the car's floor and other surfaces over the years. Some say it's more practical to scrap the car, but I can't bear to part with it because mechanically it's in such good running condition, and the body from the waist up still looks pretty good.
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Mike F - 1984 244 DL - 317,000 miles
Original engine, transmission, drive train, starter
Undergoing reconstructive surgery with POR-15

1972 142 S - The Yellow Brick - 135,000 miles
All stock except for Weber Carb. B20B engine. M40