There are numerous synonyms available for the term "seal up" which can be used in a variety of contexts. Some popular options are "close," "shut," "bar," "block," "clog," and "obstruct." Alternatively, you could also use "secure," "fasten," "bolt," "latch," "lock," or "seal off." Additionally, if you're looking for synonyms that convey the idea of protection or preservation, you may want to consider using "encase," "wrap," "insulate," or "seal in." All of these words can be used in different situations to express the same meaning as "seal up," depending on what type of context you are dealing with.