When installing outside, can you lay it over gravel, or what is a good ground prep over dirt? Also, how can you match the seems without gluing them together? That way, they don’t spread apart? Can you get bigger pieces other than 4’? I have a 20’x30’ outdoor area, and I would like as few seams as possible.

You can install our 1/4" Pre-Cut Tough Rubber Rolls over compacted gravel. If you are concerned the seams may separate for any reason, you could try and place our double-sided tape under the rolls. You would just remove the protective paper on one side of the tape. Our rubber rolls only come 4' wide. The best option would be to purchase 5 rolls 30' long to reduce the number of seams.