Although the manual that came with the set says that it is pre-stained and ready for outdoor use, I want to make sure that the table set doesn't get weathered down as it's going to be put in an area that gets a lot of rainfall. Should a clear coat do the job? What else could I do to prevent deterioration?
Welcome to the Bunnings Workshop community @newn3on. It's good to have you join us and we trust our members will provide all manner of helpful advice and project inspiration for your home and garden.
Resident Bunnings D.I.Y. expert @EricL will be back on the site tomorrow and will be happy to assist with recommending the best product for you to use.
Thanks for your patience in the meantime.
Thank you for sharing your question about your outdoor table set. Putting on another coat on the existing coat of your furniture is not advisable. Patching or an uneven finish will occur on top of your timber furniture. This is because of uneven absorption caused by the current finish on your furniture. Generally, the paint on your furniture is sanded off before you put on a new coat on top. By sanding off the old coat you'll get a uniform absorption rate from the timber furniture.
At the moment the current coat on your furniture should be sufficient to protect it from the elements. The can of sealer you've posted is for interior use only and is not suitable for outdoor use. However, if you're thinking of putting on a clear sealer, I suggest identifying first if you have a water-based or oil-based coat on your timber furniture. I suggest trying the water bead test, put a few droplets of water on top of the furniture if they bead up and don't get absorbed into the wood it is an oil-based sealer. You can also try the alcohol test, grab a cotton ball and put some isopropyl alcohol on it and rub a hidden part of the furniture. If the stain goes lighter or comes off it is water-based. Oil-based finishes don't react to alcohol.
I recommend having a look at the clear varnish sealers at the store and seeing which one is compatible with your furniture set. Please make sure that it is rated for outdoor use. Outdoor varnish sealers will have UV protection elements in them which will protect your furniture from the sun. Please make sure to test a hidden part of your furniture first to make sure that it is compatible with its finish.
If you need further assistance, please let us know.