Most bubble type solar covers are made of polyethylene, which cannot be glued by almost any type of glue. IPS Weld On adhesive #1829 might work.
Polyethylene plastic is heat sealed to join two pieces together. There are some instructions on the web for making a DIY heat sealer for polyethylene bags, or similar thin sheeting, that might work. Although, it would probably be more trouble than it's worth unless you really wanted to do it or are particularly handy at making such things.
For example, vacuum sealer bags are polyethylene and are heat sealed by the vacuum sealer machine.
Getting the heat and pressure just right without melting the plastic is tricky. You could buy an Impulse Heat Sealer, but getting one to do the length you need would be very expensive.
There might be a local company that has a suitable heat sealer that would do it for you.
Heat sealing is not very practical. You could use other forms of connecting the two pieces of material such as using plastic snap together rivets or stitching the pieces together using a stitching awl to sew them together.