Without using `\fboxsep` method, how to make a cell has 4 equal paddings?

Question

Scenario

Plese see the screenshot below. The top table is produced using minipage-typed column and the bottom table is produced using m{}.

WITHOUT using \fboxsep approach (that was already answered here), how to modify the bottom table such that it looks like the top table?

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Screenshot

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Minimal Code

\documentclass{article}
\usepackage{array,calc,longtable}

\tabcolsep=5mm
\arrayrulewidth=2pt

\newcolumntype{A}
{
     >{\begin{minipage}{0.3\linewidth-2\tabcolsep-1.5\arrayrulewidth}%
     \vspace{\tabcolsep}\centering}%
    c%
    <{\vspace{\tabcolsep}\end{minipage}}%   
}

\newcolumntype{B}
{
     @{}>{\centering}%
    m{0.3\linewidth-0\tabcolsep-1.5\arrayrulewidth}%
    <{}@{}%
}

\def\pic{\rule{2.5cm}{1cm}}
\begin{document}

\begin{longtable}{|*2{A|}}\hline
\pic & \pic \tabularnewline\hline
\end{longtable}

\begin{longtable}{|*2{B|}}\hline
\pic & \pic \tabularnewline\hline
\end{longtable}

\end{document}

Answer 1

\documentclass{article}
\usepackage{array,calc,longtable,varwidth}

\tabcolsep=5mm
\arrayrulewidth=2pt

\newcolumntype{A}
{
     >{\begin{minipage}{0.3\linewidth-2\tabcolsep-1.5\arrayrulewidth}%
     \vspace{\tabcolsep}\centering}%
    c%
    <{\vspace{\tabcolsep}\end{minipage}}%   
}

\newsavebox\TBox
\newlength\THeight
\newlength\TWidth

\newenvironment{saveTBox}[1][0.5\linewidth]
  {\begin{lrbox}{\TBox}\varwidth{#1}}
  {\endvarwidth\end{lrbox}%
   \THeight=\ht\TBox \advance\THeight by \dp\TBox \advance\THeight by 30pt
   \TWidth=\wd\TBox\advance\TWidth by 30pt
   \minipage[c][\THeight][c]{\TWidth}\centerline{\usebox\TBox}\endminipage}

\newcolumntype{B}{@{}>{\saveTBox}c<{\endsaveTBox}@{}}


\def\pic{\rule{2.5cm}{1cm}}
\begin{document}

\begin{longtable}{|*2{A|}}\hline
\pic & \pic \tabularnewline\hline
\end{longtable}

\begin{longtable}{|*2{B|}}\hline
\pic & \pic \tabularnewline\hline
\end{longtable}

\end{document}