To create a sealed join you can use this seam seal which is effectively a "super glue" for vinyl floors.
Instructions for use - full details on tube but briefly as below -
Leave the slightest of gap (1mm or less) between the 2 edges of the material when laying them out and securing them to the floor. Stick masking tape over the join and cut a strip to expose the join in the flooring. Inject the cold welding liquid until overflowing, remove excess and immediately remove the masking tape. Do not allow access until fully dried. The joint will be completely hard after only 1 hour.