How to decoupage napkins on lampshade ?

Should hold up once sealed and dry

https://www.hometalk.com/diy/decorate/rooms/sweet-floral-decoupaged-lampshade-41196783

https://www.hometalk.com/diy/decorate/rooms/pretty-pink-roses-decoupage-lampshade-up-cycle-40987323

https://www.hometalk.com/diy/decorate/rooms/beautiful-boho-patchwork-lampshade-41196117

I know our porch gets pretty damp during storms. I’d be concerned that the napkins would get too wet and fall apart.

Hi Louise. Begin with a clean surface. Use a foam brush to apply mod podge on the lamp. (work in small areas at a time) If you're using napkins, pull the top layer off of them. Only use the top ply. You could cut different shapes from the napkin if you like. Or you could rip different shapes by hand for a less formal look. OK, so apply the mod podge first. Then put your napkin on top of it. Continue this process until you have a large section complete. Then go over the work with a layer of mod podge. Continue till you're done. Once the top layer of mod podge is dry, add another coat. Do this until you have 3 or 4 layers of mod podge on it. I would put a couple layers of sealer on it, since it will be outside. Good luck Louise. Stay well.

Louise: maybe this will help

https://diyeverywhere.com/2019/06/10/how-to-make-a-decoupaged-napkin-lampshade/

Maybe you could use the outdoor mod podge?

You can use Mod Podge to decoupage single sheets of decorative napkins to the lampshade. They do make an outdoor version of Mod Podge however I am not sure the napkin would hold up.