Three weeks ago, millions of television viewers watched Denver’s Joshua Thurmond reach a deal with investor Lori Greiner on the hit show “Shark Tank.” On Monday, however, the founder of the portable campfire company LavaBox told BusinessDen he’d decided that day — nearly a year after the episode was filmed — not to sign the deal. “I did want it to work out, but it’s difficult to give up 12.5 percent of your company that you built … we’re not in dire straits on cash so it was really about her leadership and mentorship,” said Thurmond, 47. LavaBox was born three years ago when, joking with friends on a rafting trip during peak forest fire season, Thurmond got the idea to create a portable, safe campfire. He went home, and within a week created seven versions using a military-style ammo box.