Seasonality is not itself disqualifying. The test is whether the enterprise can produce more than a minimal living for the investor's family, or a significant contribution such as U.S. jobs, now or within five years, and a profitable summer business can meet it.
Marginality is about capacity, not calendar
The Foreign Affairs Manual describes a marginal enterprise as one that lacks the present or future capacity to generate more than enough income to provide a minimal living for the investor and family. Nothing in that definition requires twelve months of operation. An outfitter that books guided trips from May to September, employs four seasonal guides and a cook, and shows net income on three years of returns that would support a household is not marginal because its boats are hauled out in November.
What a consular officer will examine is whether the numbers are real: whether the income depends on the seller's personal reputation, whether the guide payroll is on the books, and whether the buyer's plan for the off-season is credible. A business that barely covers its own costs and supports the family only if the investor takes no salary is closer to marginal, and the five-year projection then has to carry the case. Present the seasonal pattern openly rather than smoothing it.